1. Field of the Invention
The present invention relates to a novel medium for image formation and more particularly to a medium for image formation which comprises a monomolecular film or monomolecular built-up film of a metal chelate compound provided on a substrate.
The invention also relates to a novel process for image formation, and particularly to a process for image formation based on the application of active energy signals to a monomolecular film or monomolecular built-up film of a metal chelate compound to control adsorption and desorption of a gas on the film or to reduce metal ions in molecules of the metal chelate compound, thereby forming an image.
2. Description of the Prior Art
Various recording media and processes are known for recording images by applying optical, thermal, or electrical energy signals. Some of these media or processes have been put into practical use (see, for example, "Insha Kogaku (Printing Technology)", II, III, published by Kyoritsu Shuppan Co., Ltd.). In particular, there are many investigations on recording media and processes using metal chelate compounds. As an example, the recording medium disclosed by J. J. Robillard [Photographic Science and Engineering, 8, 28 (1964)], which forms a visible image on image exposure with a high voltage applied, is constructed as follows: Particles of a compound (e.g. CuSCN) which produces catalytic ions on light exposure, together with a color-forming material (a metal chelate compound, e.g. Na[Co(C.sub.5 H.sub.7 O.sub.2).sub.2 (NO.sub.2).sub.2 ]) adsorbed around the particles, are dispersed in a binder; a conductive substrate is coated with a several microns thick layer of the resulting dispersion; this layer, acting as a recording film, is overlaid with a transparent plate such as a glass plate on which a transparent SnO.sub.2 electrode is formed by vapor deposition. In this medium, a colored image based on metallic cobalt can be formed by image exposure of the medium while applying a high voltage between the SnO.sub.2 electrode and the conductive substrate.
Another example of the chelate-based recording media is one disclosed in Japanese patent application Laid-Open Nos. 45,622/75 and 130,218/76. This medium is constructed by dispersing a tellurium metal chelate compound (e.g. dichlorotellurobisacetophenone) and a photosensitizer (e.g. pyrenequinone) in a binder, and coating the dispersion on a substrate. In this medium, a colored image based on metallic tellurium is obtained by image exposure followed by heating. As an example of media for image recording similarly to this by light exposure and heat treatment, the recording medium of Japanese patent application Laid-Open No. 109,720/75 is known, which comprises a .beta.-diketonito-metal chelate compound and a photosensitizer.
A further example of the chelate-based recording media is a medium developed by Eastman Kodak Co. In this case, the image formation process is similar to the above; that is, a colored cobalt chelate image is reproduced by light exposure and heat treatment. As a modified example, there has been proposed a technique of color formation on a diazo paper by utilizing ammonia gas evolved from said recording medium during the heat development. More specifically, this recording medium is constructed by dispersing a hexamine cobalt III complex ([Co(NH.sub.3).sub.6 ].sup.3+ 3Cl.sup.-), a photosensitizer (e.g. quinone), and a compound (e.g. 1-(2-pyridylazo)-2-naphthol), hereinafter abbreviated as PAN) capable of forming a colored chelate jointly with cobalt ions, in a binder, and coating the dispersion on a substrate. On heating after image exposure of this recording medium, the cobalt in the exposed portion is reduced from trivalent to divalent and the divalent cobalt ion, jointly with the PAN, forms a chelate. This chelate undergoes a ligand exchange reaction with the hexamine cobalt complex (III), yielding a colored chelate of trivalent cobalt with PAN. The reaction chelating a divalent cobalt ion with completely free PAN is repeated to a yield the trivalent cobalt-PAN colored chelate according to a chain reaction, thus forming a visible image.
A still further example of the chelate-based recording media is a medium constructed of a supported layer of a mixture of a metal salt of higher fatty acid and a compound capable of forming, jointly with the metal of said salt, a colored chelate, dispersed in a binder, or otherwise two supported layers containing separately these compounds dispersed in a binder, wherein a colored image is developed corresponding to the recorded image by heating the medium to fuse together the metal salt and the chelating agent. For instance, a combination of zinc stearate with diphenyl carbazone gives a red image and the combination of ferric stearate with gallic acid gives a black-purple image.
These prior techniques, however, have the drawback of forming much blurred or fuzzy images because the thickness of the recording layer is as large as several microns in any of these media. Another drawback of these media is that when the recording layer is to be formed of a dispersion of recording compounds in a binder, coating operation using a solvent is necessary to apply the dispersion and the color forming reaction partly occurs during the coating step, this tending to cause so-called fogging. When recording compounds are distributed separately in plural recording layers in order to inhibit the above undesirable reaction, another drawback arises in which the efficiency of the reaction between these compounds is markedly lowered and further the resolution of images and the sensitivity are notably deteriorated. Additionally, when voltage application across these recording layers is necessary, a high voltage (e.g. several hundreds of volts) is required since the recording layers are thick as a whole.